Abstract: DH36 steel is widely used in China currently as high strength hull structural steel. This paper adopts carbon replica, XRD diffraction, TEM observation and analysis method of controlled rolling and controlled cooling after the DH36 steel nano precipitates of type, morphology, size and number are analyzed in detail. The results show that the morphology of the precipitates in the microstructure of DH36 steel for the rules of the square, which is composed of (Ti, Nb) (C, N). The test of DH36 steel carbonitride precipitation volume fraction of the matrix is 0.00957%. The total contribution to the precipitation strengthening and fine grain strengthening is 211.24 MPa and 212.30 MPa Solid solution strengthening is 122.93 MPa and dislocation is 134.43 MPa.